Implementation of probe rheology simulation technique in atomistically detailed molecular dynamics simulations

Abstract

The probe rheology simulation technique is a technique for measuring the viscosity of a fluid by measuring the motion of an inserted probe particle. This approach has the benefit of greater potential accuracy at a lower computational cost than other conventional simulation techniques used for the calculation of mechanical properties, such as the Green–Kubo approach and nonequilibrium molecular dynamics simulations, and the potential to allow for sampling local variations of properties. This approach is implemented and demonstrated for atomistically detailed models. The viscosity of four different simple Newtonian liquids is calculated from both the Brownian motion (passive mode) and the forced motion (active mode) of an embedded probe particle. The probe particle is loosely modeled as a nano‐sized diamond particle: a rough sphere cut out of an FCC lattice made of carbon atoms. The viscosities obtained from the motion of the probe particle are compared with those obtained from the periodic perturbation method, and good agreement between the two sets of values is observed once the probe‐fluid interaction strength (i.e., εitalicij in the pair‐wise Lennard–Jones interaction) is two times higher than their original values, and the artificial hydrodynamic interactions between the probe particle and its periodic images are accounted for. The success of the proposed model opens new opportunities for applying such a technique in the rheological characterization of local mechanical properties in atomistically detailed molecular dynamics simulations, which can be directly compared with or help guide experiments of similar nature.

Drag on nanoparticles in a liquid: from slip to stick boundary conditions

“…39 The breakdown of Stokes' law may be attributed to the increase of fluid viscosity in the vicinity of the particles 40 or a failure of the continuum approximation. 41 Besides the stick boundary conditions, slip boundary conditions have also received extensive attention. [42][43][44] It has been indicated that smooth particles follow Stokes' law with slip boundary conditions, whereas the stick boundary conditions are valid for rough particles.…”